1. Field of the Invention
The present invention relates to a method for forming a metal layer of a semiconductor device, and more particularly, to a method for forming a metal layer of a semiconductor device using a metal halide gas.
2. Description of the Related Art
As the density of semiconductor devices increases, the design rule gradually decreases. Accordingly, the aspect ratio of contact holes increases while the junction depth becomes shallow. The junction depth is closely associated with a short channel effect of MOS transistors. In particular, MOS transistors suitable for high integration semiconductor devices need a short channel. In addition, to improve the characteristics of a MOS transistor with such a short channel, the depth of a source/drain region, i.e., the junction depth, must be formed to be shallow. An interconnection technology to achieve a shallow junction employs a metal barrier layer to prevent junction sparking where a metal interconnection penetrates the shallow junction. Also, an ohmic layer is interposed between the metal barrier layer and the junction.
Commonly, the ohmic layer is formed of Ti and the metal barrier layer is formed of TiN. These layers are formed by chemical vapor deposition (CVD). For the CVD, TiCl4 gas is used as a metal source gas. However, if the TiN layer is formed using TiCI4 gas, the TiCI4 gas may react with the Ti layer, which is underneath the TiN layer, thereby resulting in chlorine (Cl)-containing lumps on the Ti layer. To solve this problem, after the deposition of Ti layer and before the deposition of the TiN layer, the surface of the Ti layer may be nitrified. As a result, the overall process is complicated. Furthermore, if the Ti layer is too thick, the Ti layer corrodes even though the nitridation is performed.
To solve the above problems, it is an objective of the present invention to provide a method for forming a metal layer of a semiconductor device using a metal halogen gas, in which a metal underlayer formed underneath the metal layer can be protected from degrading by a halogen component of the metal halogen gas.
According to an aspect of the present invention, a method for forming a metal layer of a semiconductor device, comprises forming a metal underlayer on a semiconductor substrate; supplying a reaction gas having a higher reactivity with an active halogen element of a metal halogen gas, than a metal component of the metal halogen gas, into a reaction chamber; and supplying the metal halogen gas into the reaction chamber to deposit the metal layer over the metal underlayer.